To illustrate this, I'm going to start by using India and Pakistan. Long long ago, they were largely one entity under British rule. Then come independence. Muslims demanded a separate state to protect themselves from religious persecution, Hindus I believe preferred it whole, well because they were always Indian. The poms in all their wisdom granted this separate state wish, whereupon mass upheaval and uprisings followed. Lots of people died.
The jews also requested a homeland in the Middle East because of the holocaust and their long history of religious persecution, so the territory under British control was ceded to the jews to create the state of Israel. Never mind the people already living there peacefully under nominal British rule, Jews, Muslims, Christians et al. Under the highbrow intentions of welfare for a religiously persecuted group we now have all the anguish and bloodshed today.
Hong Kong was officially British till the end of time, but in the interest of good optics was given back to China. Well you can ask the Hongkies how that went.
I can go on, but let's come back to bolehland and sinkieland. When independence was granted in Malaysia, there was some form of enshrining Malay/Muslim pre-eminence into the legal constitution or framework as part of their well-meaning departure at that time. I figure there were some shenanigans involved with Singapore because they were granted independence at different times. But in the end, LKY was in a desperate enough situation back then that he felt that he needed Malaysia, and so I believe he made Malay the official language, anthem in Malay etc and enshrined their rights and their special status semi-officially to be allowed into the Malaysian fold.
My apologies for not knowing more about the local situation. I glean my info from true scholars of full history warts and all which in Singapore tends to be a bit scarce. The official version rarely mentions all the ugly details.
So in short, the British with their mighty empire were well-intentioned, but just largely listened to special interest groups (ugh I hate that bunch of people), so gave rise to the problems in the world still in existence today.
edit : oh I forgot that stupid India/Pakistan division thing, there are more Muslims living in India than in Pakistan. That's how dumb the whole idea was. And if I wasn't clear above, the non-Paki's preferred it whole, Hindus and some Muslims.